Ultrasound imaging of various aspects of the heart is a well known diagnostic modality. Systems have been designed which enable an ultrasound system to determine the volume of the left ventricle of the heart at various times during the cardiac cycle. Such imaging systems enable identification of a tissue/blood interface and allow a physician to trace the interface and perform calculations regarding blood pumping efficiency and volume. Such systems require an ability to accurately identify the endocardium/blood boundary. In U.S. Pat. No. 5,195,521 to Melton, Jr. et al., assigned to the same assignee as this application, a majority vote circuit indicates, at each range along an ultrasound-scan line, when a majority of the signals for both a current scan line and two previous scan lines indicate that reflections of the transmitted pulses are from tissue or blood. In this manner, the tissue/blood interface is accurately determined and is less affected by noise.
U.S. Pat. No. 5,257,624 to Fraser et al. and assigned to the same assignee as this application, describes a gain control circuit which enables gain along one or more scan lines to be kept substantially constant--thereby enabling a more accurate tissue/blood boundary determination. The accuracy enhancement occurs because the boundary judgement is based upon a discrimination in levels between return pulses, with tissue generally returning a higher level signal than blood. If the gain of return signals from a scan line varies significantly due to tissue attenuation, tissue/blood boundary determination is rendered substantially more complex.
U.S. Pat. No. 5,322,067 to Prater et al. (assigned to the same assignee as this application), describes an improved technique for determining volumetric efficiency of the left ventricle. An ultrasound display of the left ventricle and surrounding tissue is obtained and the user traces a region of interest around the ventricle at the largest volume for which a volume determination is to be made. Each pixel of the ultrasound image within a region of interest is classified as a blood pixel or a tissue pixel. The area of blood pixels within each display frame is determined and the volume of the ventricle is calculated from the area of the fluid pixels within each segment of the region, using the method of disks.
In U.S. patent application Ser. No. 08/308,718 to Koch, III et al., pixel changes from tissue-to-blood or blood-to-tissue are determined over succeeding display frames. For each pixel evidencing a like kind change, a common mapping function is assigned so that all such changed pixels exhibit a common appearance. In the preferred mode, the common appearance is a single color assigned to all changed pixels of a same type (e.g., blood-to-tissue) in a frame. When succeeding frames are compared, there is a binary change in pixel color values between pixels which change type from one frame to the next. Tissue/blood interfaces are thereby clearly visible.
The cardiologist, in assessing heart function, often wishes to know the pumping efficiency of the left ventricle. Existing ultrasound systems require the user to trace the outline of the pumping chamber by generating a boundary around this region of interest with an input device such as a mouse or track ball and to input the traced outline into the system. By knowing the cross section area of the chamber at diastole and systole, the system is than able to determine volumetric changes. Such outline tracing may be time consuming and laborious. Accordingly, there is a need in modern ultrasonography systems for a quick method of constructing a region of interest outline about an ultrasound image and for making flow or volumetric change calculations with respect thereto.